
\chapter{A Night on the Bare Mountain}

\section{Observer's hardware}

When you arrive at the control room of the telescope, you will be 
confronted with a series of displays (figure 4.1). You will mainly need to be 
aware of

\begin{figure}[p]
\vskip 20cm
\caption[INT control room]
{INT control room}
\end{figure}


\begin{itemize}
\item The observer's VDU. Observing is controlled from there. You issue 
      the commands that {\em control} the spectrograph, A\&G box and detector,
      once they have been configured (after physically changing gratings and
      collimators).

\item The MIMIC display (figure 4.2) is a schematic picture of the A\&G box 
      and the spectrograph, showing the status of all relevant components.
      It is a very useful mnemonic, as tracing down the light path you will
      encounter everything that matters between the Cassegrain primary aperture 
and the detector.

\begin{figure}[p]
\vskip 20cm
\caption[MIMIC display]{MIMIC display}
\end{figure}

\item The LEXIDATA display and joystick box. This is where you see the data.
      The joystick controls the cursor. The switches on the box are used to 
select alternatives and initiate actions in some graphics programs.
\end{itemize}

\section{Introduction to the CCD system}

The camera system - shown in figure 4.3 - consists of the following parts:
\begin{itemize}
\item The liquid nitrogen cooled camera head which is mounted at the appropriate
spectrograph focus.

\item The analogue drive box which is mounted within about 2 metres of the
camera head.

\item The digital controller which is located off the telescope and interfaced
to the instrument computer.  For data collection the instrument computer uses a
disk (and tape) with Lexidata display.

\end{itemize}

\begin{figure}[p]
\vskip 20cm
\caption[CCD Camera system]
{The CCD Camera components}
\end{figure}

The camera head is an evacuated cryostat which supports (and cools) the
CCD behind an anti-reflection coated fused silica window.  A preamplifier and
temperature controller are attached to the cryostat.  There are no moving parts,
except the three-point kinematic mount which provides focus and tilt
adjustment manually.  The drive box contains CCD clock drivers,
analogue-digital conversion and associated electronics.

The controller box is programmable via the instrument computer to define the
particular mode of operation of the camera; it is linked via a CAMAC module to
the Instrument Computer.  No electronic adjustments should normally be necessary
to the camera system.

Details of camera set-up and routine observations are given in the following 
sections.

\subsection{CCD format}


Figure 4.4 shows the CCD format, and some associated information.  The
size of the image area (and in fact the ``underscan'') are fixed when the chip 
is manufactured.  The size of 
``overscan'' in both directions could be varied if required.

\begin{figure}[p]
\vskip 20cm
\caption[CCD format]
{CCD format}
\end{figure}

The CCD is mounted with its long axis (horizontal) in the dispersion
direction.  Row 1 is read out first and appears at the top of the LEXIDATA
screen - this is blue on the 235 camera and red on the 500 camera.  (Note that
the CCD does not maintain the same dispersion direction on both cameras, unlike 
the IPCS).

It is possible to read out a reduced window of the CCD frame, although the
full-frame is recommended for all work at present.
 
For the GEC CCDs columns 1-11 are ``underscan'' and not subject to 
illumination; they can be
used to give a zero reference level for the data frame.  Columns 12-396 are
true image elements.  Columns 397-400 are ``overscan'', as are rows 579-580;
these elements contain residual signal and give a measure of any poor charge
transfer efficiency in both directions - this can be ignored.

\subsection{Signal levels, noise and dynamic range}

The CCD signal charge is converted to a voltage, amplified and digitised;
the computer measures the signal as an analogue-digital conversion unit (ADU).
The readout of any signal charge from a pixel has an intrinsic associated
electrical noise (see Table~2.1).

There is an artificial, but necessary, electrical offset to the measured
signal; this ``bias'' has a mean level of 100-200 adu but needs to be measured
since it is subject to a small drift (up to 10 adu from night to night).

The CCD integrates all light that falls on it and is not subject to any
limitation of photon rate.  The recommended maximum signals (for linearity) are
$\sim$30,000 adu/pixel, although saturation (at 65,535) is permitted without
damage.  Thus the dynamic range (from max. signal to 3$\sigma$) is about 10000.

\subsection{Preflashing}

Some chips currently in use suffer from a threshold effect such that signal
charge below a certain level cannot be transferred within the CCD and therefore
cannot be measured.  In order to enable weak signals to be measured the CCD is
subjected to a brief flash of illumination prior to each exposure.  It has been
empirically determined that a normal preflash of 40 units is
sufficient to give good results for the GEC4 chip (this chip has already been 
replaced with GEC6).
A lesser preflash would not allow weak sources to be correctly detected
and a larger preflash increases the Poisson shot noise without significant
signal gain.

The normal preflash gives an average signal level of $\sim$25 adu above the 
``bias'' level; this corresponds to $\sim$25 e$^-$, with an
associated shot noise $\sim$5 e$^-$. Thus the total effective ``readout'' noise 
(with preflash) is $\sigma \sim 8 e^-$, this is measured as an rms noise of 8
adu.

The preflash illumination is not uniform and increases towards the edges
of each row - see Figure 4.5. The level of preflash is however reasonably
uniform down the centre of the CCD where a dispersed spectrum would normally
lie.

\begin{figure}[p]
\vskip 20cm
\caption[Preflash frame]
{A preflash frame obtained with the GEC4 chip in March 1989}
\end{figure}

Figure 4.6 shows several 1000 second long-slit exposures of NGC 3310 (a galaxy
with a circumnuclear ring of star formation) with GEC4 covering 
3650-9700\AA . This example shows the various charge traps as dark columns.
Cosmic ray events appear as bright spots.  The dispersed spectrum of the object
is seen falling-off towards the red wavelength end.  Some night sky emission
lines are seen. These frames have  not had the preflash subtracted
and so this modulation of the background is also visible.  Figure 4.7 shows the 
corresponding line-plots.

\begin{figure}[p]
\vskip 20cm
\caption[(a) NGC~3310 spectrum around $\lambda$ 4300 \AA ]
{(a) Unprocessed frame of a 1800 s long-slit exposure of NGC~3310 with 
$\lambda _c$ 4300 \AA ; notice dark columns,  bright spots, sky emission lines
and [OII] $\lambda$ 3727 \AA .}
\end{figure}

\begin{figure}[p]
\addtocounter{figure}{-1}
\vskip 20cm
\caption[(b) NGC~3310 spectrum around $\lambda$ 5400 \AA ]
{(b) Unprocessed frame of a 1300 s long-slit exposure of NGC~3310 with 
$\lambda _c$ 5400 \AA ; notice \hb\ and [OIII] $\lambda\lambda$ 4959,5007 \AA .}
\end{figure}

\begin{figure}[p]
\addtocounter{figure}{-1}
\vskip 20cm
\caption[(c) NGC~3310 spectrum around $\lambda$ 6600 \AA ]
{(c) Unprocessed frame of a 1000 s long-slit exposure of NGC~3310 with 
$\lambda _c$ 6600 \AA ; notice \ha\ and [NII]}
\end{figure}

\begin{figure}[p]
\addtocounter{figure}{-1}
\vskip 20cm
\caption[(d) NGC~3310 spectrum around $\lambda$ 9000 \AA ]
{(d) Unprocessed frame of a 1800 s long-slit exposure of NGC~3310 with 
$\lambda _c$ 9000 \AA ; notice dark columns,  bright spots, sky emission lines
and [SIII] $\lambda \lambda$ 9069,9532 \AA .}
\end{figure}

\begin{figure}[p]
\vskip 20cm
\caption[1-D sample spectra]
{Line spectra extracted from the frames in Figure 4.6; these are the final 
product} 
\end{figure}

\section{Set-up}
\subsection{Technical preparations}

Local technical support would have prepared the cryostat before an observing
run. This preparation includes cryostat evacuation and filling with
liquid nitrogen (check with the telescope operator). It also includes the 
cryostat mounting and adjustment as follows.

\subsection{Cryostat mounting and adjustment}

The cryostat may be mounted on the 235 or 500 mm cameras; in both cases it
is fitted in the same orientation - with its fill tube uppermost above the
horizonal axis.  A circular mounting ring is bolted onto the spectrograph -
this clamps the cryostat with a three-point kinematic location; it allows a
tilt/focus adjustment as well as rotation of the cryostat (figure 4.8).

\begin{figure}[p]
\vskip 20cm
\caption[Cryostat mounting plate]
{A shematic drawing of the cryostat mounting ring}
\end{figure}

Rough focus, rotation and tilt should only need adjustment when the camera
head is changed.  This is a difficult process which is performed by local
technical support. Fine focus (with collimator) should be checked each night and
when extreme grating angle changes are made.  It is possible to remove
the CCD cryostat and then replace it on the same spectrograph camera without
adjustment.

The appropriate CCD field-flattener lenses for each camera must be used.
On the 235 camera only an additional 3mm aluminium spacer ring is used.  When
fitting the mounting ring to the spectrograph take care not to adjust any
spectrograph mirror screws!

For the recommended micrometer settings, see the CCD Log-Book in the control
room. The micrometers read to 0.01mm, with 0.50mm per revolution.
In order to adjust any of the three support points it is important to back
off all three micrometers to avoid damaging them, as they are for reading the 
position {\bf only}.  The tightening knobs should be slackened {\bf slightly} 
to allow the three capstan screws to jack the cryostat in or
out.  One revolution of the capstan = 0.63 mm. (The micrometers are shortly 
to be replaced by  an electronic sensor).


Clockwise rotation of the capstan screws moves the cryostat outwards and
results in a reduced micrometer reading.  This corresponds to a positive
Hartmann shift if measured Left (HARTMANN 0 1 or OUT IN) then Right (HARTMANN
1 0 or IN OUT)
The cryostat is only retained in place by the three clamping knobs so take
care to support it when they are loosened.


\subsection{Logging in}

The first thing to do, on approaching the Instrumentation Computer, is to
log into it and start up ADAM. This is also described step by step in 
Section~4.4 (pink pages).

\begin{itemize}
\item Check that the system is clear of all other users.  Ask, if in
doubt.

\item Sign on (log in) using the SI command.  You should have been
allocated a user number (n) in the range 1 to 8; write it down on the board.
Use up to four initials to identify yourself.
\begin{verbatim}
           SI <initials>,<n>,<n>
\end{verbatim}

If you encounter any difficulties, there may be somebody still logged in
at the terminal, so try the command 
\begin{verbatim}
           SO 
\end{verbatim}

      and retry the SI command. 

\item Now, to run ADAM, type 
\begin{verbatim}
           ADAM
\end{verbatim}

\item ADAM should now start up and present you with a two level menu.  The first
choice is the focus at which you are observing (CASS), and the
second is the instrument/detector combination IDS/CCD. 

\item The system now loads the relevant software for your selection and performs
some initialisation. You need to answer some questions about the gratings etc.
which are fitted to the spectrograph. The computer has no knowledge of these
options, but only a memory of what it was last told. If, e.g.~a collimator has 
been changed, you must say so; the support astronomer
will have physical access to the spectrograph to change gratings and 
collimator. Eventually the VDU gives an ADAM prompt 
\begin{verbatim}
           Adam:>
\end{verbatim}
\end{itemize}

You can now use any of the ADAM commands described in the next chapter. 

\subsubsection{Break in}

If, for any reason, ADAM goes dead and you don't get the ADAM:$>$ prompt,
try the SEND CON: command. It has a similar effect to  $<$CTRL/Y$>$ or $<$CTRL/C$>$ 
on the VAX. CON: is a mandatory parameter, and is the name of the ADAM terminal.

This command should only be used when there is no ADAM prompt.  It can be
issued at other times (e.g.~to halt a command that is producing a lot of 
output), if you first press the BREAK key and the Operating System's ``*'' 
prompt is obtained.

Sometimes it is necessary to type an extra c/r to make the command work.
On rarer occasions it may be necessary to issue the command more than once for
it to take effect. If it still does not work, type CANCEL and then start ADAM 
again.

\subsection{Rotation alignment}

Data reduction is greatly simplified if the dispersion direction is along one CCD 
column. A check for rotation of the CCD can be performed as follows.
It is best to use a high dispersion (600 or 1200 lines) grating set for the red
(6000-8000 \AA ).

\begin{verbatim}
     IDS OPEN        (camera shutter open)
     DEKKER 1        (narrow dekker) with IPCS dekker; DEK 3 with FOS dekker
     TUNG ON
     COMPMIRROR IN   (light from calibration lamps through the IDS)
     SLIT 180
     GLANCE 10       (a 10 sec trial exposure)
     PHOTOM          (to take a horizontal profile)
\end{verbatim}

Use PHOT to take horizontal profiles (figure 4.9)
at (a) and (b), i.e. near top and
bottom of detector.  The effective line centres are printed out.
It is best to take the profiles
over only about 10 elements and perhaps to sample in one or two places at top
and bottom.  It is possible to align the rotation to within 0.1 or 0.2 pixel
over the length of the CCD.  This method gives 
good setup of rotation; it assumes that
the slit is normal to the dispersion direction.

Rotation adjustment if necessary, is achieved by manual movement of the
cryostat;
the mounting ring has six slotted holes for this purpose (figure 4.8).
The 6 bolts should be slightly
released and the cryostat should be rotated out of position so as to approach
the ideal position in one direction only.  
The micrometer D should be used only to measure rotation position (not to move
the cryostat) although a small degree of backlash/flop can be
experienced.
An increase of 0.35 mm in the micrometer reading will rotate a dispersion
column by about 1 pixel in 500 anticlockwise. The rotation normally only needs
setting when the CCD is first installed on the camera, and this will be done
by a DT or a SA. Observers should not attempt to make these adjustments
themselves.

\subsection{Tilt adjustment}

A check to ensure that the CCD is parallel to the focal plane of the
spectrograph follows. By using the routine TILT which is
fairly self-explanatory inside the SETUP mode (see 
section 4.4) one can check that the focus is the same
at six different windows. The positions of these windows should include
bright arc-lines. In the red, with a high dispersion grating, CuNe lamp is the 
best one. 

\begin{verbatim}     
     DEKKER 0 
     1LAMP ON
     SLIT 185
     other settings as before

     GLANCE 10
\end{verbatim}

Following the Glance run check the existence of two intense arc-lines near 
the top and bottom of the chip. See figure 4.9. Then

\begin{verbatim}
     SETUP            (Loads software for TILT and FOCUS)
     TILT             and answer prompts.
     exposure time > 10 secs. (when prompted).
\end{verbatim}

\begin{figure}[p]
\vskip 20cm
\caption[SETUP procedure]{Schematic SETUP procedures}
\end{figure}

This routine then does two exposures opening one Hartmann shutter at a time 
(first LEFT then RIGHT) and finally
prints out the shift at 6 positions as above.  Note that there is a variation
due to the effects of pixel-sampling, i.e. if TILT is repeated shifts may
vary by .05 - 0.1.

Tilt correction is achieved by adjusting cryostat screws with care. 
Approximately  1/2 turn clockwise of screws
A, B or C will increase the tilt vectors
by $\sim$1 line shift. Screw B should tilt the cryostat (and CCD) about its 
long axis, aligned
with the dispersion direction.  It is not possible to adjust tilt without
modifying the focus, but hopefully this adjustment should rarely be needed.  A
change in focus (or tilt) of about 0.1 or 0.2 (Hartmann shift) across the CCD
does not seem to be significant; and indeed very time-consuming to perfect.

Referring to Figure 4.8 again, slacken the three locking nuts before attempting
to adjust the cryostat position. Movement is effected by the capstan screws.
Also remember that the micrometers are for {\bf reading only}, and cannot move
the cryostat i.e.~back off the micrometer, adjust the capstan and then gently
screw in the micrometer and take a reading. For spectroscopic work it is the 
top-bottom (dispersion) tilt that is most important and for this adjust 
capstan B. On the 500 mm camera it is found that turning B anticlockwise
by 1 $1/4$ turns, increases top-bottom by 1 pixel.

The best way of being confident about the ``tilt'' Hartmann shifts provided
is to do two tilt set-ups without adjustment between them.  The results should 
be similar in both cases. As with ROTATION, this work should only be done by
a DT or a SA and is only necessary when a camera change has occurred.

\subsection{Focus}


This would normally be done with the grating to be used for observation  -- 
some gratings are not flat so you cannot guarantee the focus from one grating
to another.

The prompts in FOCUS (at the SETUP mode) are self-explanatory.  Use a widened 
slit ($\sim $ 300 $\mu$ m) to spread the image over several pixels, for accurate 
line centering. Follow the steps in Section 4.4 (pink pages).

A collimator auto focus routine then occurs in which five collimator steps are 
taken.  A centre-of-gravity line centre is found in order to determine the 
Hartmann shifts (it was found that the cross-correlation technique depended too
critically on the correct arithmetical signal levels).  The optimum focus is
determined automatically.  Finally, type READY to return to normal CCD
operations.

\vfill
\newpage
\section{Observation routine}

Having finished the set-up, you are ready to observe. This Section goes first 
over some general concepts and then takes you step by step through your 
observation routine.

If disk only is selected as the data destination then the number of available 
CCD
runs will be limited by the disk space.  CCDSPACE will tell you how much disk
space is still available. It is important that users
should copy important images to tape as soon as possible and then PURGE so 
that disk space is not limited.  Better still, select tape as the dump device 
so that every exposure is automatically copied to tape. After the D-tape has 
been copied to a C-tape by support staff (or the observer if he has time!), 
the disk can be purged and overwritten if necessary.  The EAGLE 
disk has space for $\sim$ 500 CCD runs. At least 60 CCD images can be
stored on a 2400 foot tape (1600 bpi).  The tape writing gives a slight
overhead to the duration of an observation - although the next one may be
started during tape writing.  However, the Lexidata must not be used whilst
tape writing proceeds. Only if you have many short exposures may you choose to 
dump the data to disk and then FITSOUT the runs to tape at the end of the night.
But remember that the data is {\bf not} safe until it has been written to tape.
The EAGLE disks failed twice in 1988 with loss of all the data on the disk in 
both cases.

An estimate of the bias level is used by the software when it does
correlations or similar operations.  This bias level is an electrical zero
offset within the CCD camera and can be measured from the ``underscan'' portion
of an exposed image (see Appendix B). The bias level may be measured using
PHOTOM/STATS after taking the first exposure, and the software default may be
corrected if necessary (using a command BIAS {\em b} where {\em b} is the 
value to be entered).

If preflash is needed for your chip (find out from your SA) the level should 
be set for all observations.  At present the default is zero, use 
PREFLASHDEFAULT=n to reset the default.

The normal high-level command that is used for an observation is of the
form RUN~t~``NAME'', where t is the exposure time in seconds and NAME is your
object.  Several (n) equal exposures  (of t seconds) can also be obtained using 
the command MULTRUN~n~t~``NAME''. Such exposures are
recorded on a sequential series of disk files and would be written to tape, if
selected.  An alternative method for a trial exposure is to use GLANCE t, where
the image is put in a scratch-file which is overwritten by the next GLANCE.
This image can be kept permanently if desired, by using the command 
KEEP~``NAME'' before another GLANCE is performed.

A RUN consists of various lower-level operations as follows:  telemetry
check, clear chip, timed exposure, readout to disk, display, (copy to tape).
The above operations take about 1, 4, t, 30, 5 (and 60) seconds respectively.
The PHOTOM and SPECTRUM utilities make available several basic image/data 
analysis options for use by the observer.  There are also other more general 
facilities such as image arithmetic operations, IPCS external memory usage, etc.
Chapter~5 summarises the ADAM software commands.

No temperature reading or other monitoring of the CCD camera is provided
directly.  The remote telemetry is automatic and only becomes visible to the 
user if a fault develops (see also the ADAM command TELEM).

After initializing the system and doing the SETUP, the following frames 
should be obtained:
\begin{description}

\item [The zero bias frame] - a 0 second exposure with preflash = 0.  In fact
about 10 of these can be taken and averaged to give best results.  This yields
a frame which records any modulation of the zero level, which should be small
($\leq$ r.m.s. noise level $\sigma$).  The centre of a single frame can be 
examined using PHOTOM/STATS to check the performance.  The mean level 
should be = ``bias'' ($\pm$ 10) with a $\sigma$ of 5-6 (e.g. over an 11 x 
11 box).

\item [A preflash frame] - a 0 second exposure with normal preflash.  This
should give a central mean value $\sim$ ``bias'' + 25, with $\sigma \sim 8$.  
The shape of the preflash should appear similar to the standard example 
(section 4.2). Take several and average.

\item [A preflash map] -  a zero second exposure with preflash = 400 (for 
normal preflash=40).  Use the
SETFLASH 400 command.  This provides a map which may be scaled and subtracted
later.  The chip readout will automatically restore the preflash to the nominal
value (now zero).

\item [A flat-field] - a tungsten flat-field may be taken although a diffuse 
sky flat-field is
much better.  Note that without corrections the pixel-pixel response variations
should be $\sim$2\% r.m.s.

\end{description}


\subsection{Afternoon Activities}
\begin{list}%
 {--}{\setlength{\rightmargin}{\leftmargin}}

  \item  Contact your SA (from Residencia, use radio or intercom to
         ask for Duty Officer)  [CCD should be on and cooled, TILT and ROTATION
         checked.] 

  \item  {\bf{COMPUTERS.}}\\                      
         Start up Perkin-Elmer ICS3220 if necessary
         (will give "$\ast$" prompt).\\
         (See notes on wall by system console, in the tape-drives room)

  \item  {\bf{LOGIN.}}\\                                       
         Check that the system is clear of other users, ask if in doubt.\\
         SI XYZ,n,n  (write initials on board and dates resident)\\
         ADAM
  \item  {opportunity to change grating, collimator, etc.}
  \item  {enter next archive image no. (for Grinnell TV images)}
  \item  {enter chip installed (e.g.~GEC3)}
  \item  {dump to disk}
  \item  {take default bias setting for now, or use value on board}
  \item  {check MIMIC display; is everything okay?}
  \item  {EXGRAT  (to improve encoder accuracy for grating angle)} 
  \item  if PREFLASH is needed (check with your SA) type:
\begin{verbatim}
        PROC CORRE T    
        SETFLASH 40        (if that is the advised value)
        RUN T "NAME"    
        END PROC
\end{verbatim}
and
\begin{verbatim}
        PROC MIRA T    
        SETFLASH 40
        GLANCE T
        END PROC
\end{verbatim}
        use these procedures instead of RUN or GLANCE.\\
        ENABLE the flash at the CCD camera head.
        
  \item  type in the following 2 procedures:
\begin{verbatim}
        PROC ARCON      
        IOPROCEED 1
        COMPMIRROR IN   
        1LAMP ON           this will be normally the CuAr lamp        
        IOPROCEED 0		
        END PROC
\end{verbatim}
and
\begin{verbatim}
        PROC ARCOFF
        IOPROCEED 1
        COMPMIRROR OUT
        1LAMP OFF
        IOPROCEED 0		
        END PROC
\end{verbatim}
	 (if you want CuNe instead, normally you have to type 2LAMP)\\
	Use PUT (and GET) to save (and retrieve) your procedures, otherwise they
        are lost each time you exit ADAM.	    

  \item  {\bf{FOCUS.}}\\         
        If you are going to use more than one collimator or grating,
        check that the focus has not changed with each configuration.\\
        NOPACKETS \hspace{.3in} (saves time during set-up, but
        remember to turn back on to observe using NOPACKETS=0)\\
        GLANCE 0 \hspace{.5in} and use PHOT in STATS mode to
        determine bias level, b.  Then\\
        BIAS b\\
        GSMOVE OPEN \hspace{.5in} (opens grating shutter)\\
        IDS OPEN \hspace{.5in} (opens spectrograph shutter)\\
        GRAT$\_$ZERO 89.75 \hspace{.5in} (check board for current
        value, check it using known arc lines.)\\
        CENWAVE $\lambda$ \hspace{.5in} (where $\lambda$ is in
        $\AA$).  You will need 2 strong, unconfused arc lines
        near the ends of the chip for focussing.  Use the arc
        plots to help you choose.  With CuAr, $\lambda$7500 is
        a good region.\\
        SLIT 300 (150) \hspace{.5in} for 235 (500) cameras.\\
        ASCF 2 \hspace{.5in} inserts GG495 for red observing
        (to cut out 2nd order blue).\\
        ASND 0\\
        ND 0 \hspace{.5in} (arc filters not usually needed with
        CCD).\\                                             
        GLA 5 \hspace{.5in} (use a double length period for the
        Hartmann exposures) and then examine spectrum with\\
        PHOT \hspace{.5in} to make sure the lines are not
        saturated.\\
        Lexidata buttons are :\\
\begin{tabular}{||l|l|l|l|l|l||}   \hline
Exit & Mode & Down & Reset & Up & BLUE \\ \hline
\end{tabular} \\
        The BLUE button is used to mark the cursor position.\\

        {\bf{SETUP}} \hspace{.5in} (makes ROT, TILT and FOCUS available
        for use; note that a FOCUS adjustment has to be made after
        checking ROT and TILT)\\
        ROT \hspace{.5in} Should already have been set (see 4.3.4)\\
        FOCUS \hspace{.5in} performs Hartman tests for 5 collimator
        positions (or just 1 if a step of 0 is used).  Note that
        shifts are given in 1/10 pixels.  Takes about 15 mins.\\
        An alternative procedure if you have problems with FOCUS is\\
        TILT \hspace{.5in} also performs a Hartman test (but
        for the current collimator position only).  For the 2
        chosen lines it gives, in addition to the mean shift,
        the L-R (along slit) and T-B (along spectrum) shifts.
        These should already have been minimised when the CCD
        was first set up by the SA.  Hence minimise the mean
        shift by trying several collimator settings, using\\
        COLL n \hspace{.5in} (where n should be in the range 170
        - 240.)\\

        {\bf{READY}} \hspace{.5in} (to return to observing mode).\\

  \item {\bf{FLAT FIELD}}\\
        This is potentially dangerous if the IPCS is also up.
        Check the Mimic display and keep an eye on the HP  display.\\
        Use the TUNG lamp at CENWAVE 7500 and some ND (1-2) with
        a wide ($\geq$200$\mu$) slit to minimise dust streaks.
        However, you should also do a flat field at your observing
        setting to calibrate any such streaks.  (Note that issuing
        TUNG will automatically set ND to its maximum value; you have to 
        adjust them.)\\
        \\ 
        Do flat field in second order ( i.e.~CENWAVE 14000)
        if low dispersion grating is used.
\end{list}
\bigskip
\subsection{Twilight/Evening Activities}
\begin{list}%
 {--}{\setlength{\rightmargin}{\leftmargin}}

  \item {\bf{TAPE.}}\\
        Mount latest D tape, and record in log book in computer room.\\
        DATA \hspace{.5in} (and answer questions).
        If integrations are short or MULTRUN is in use, then
        just dump data to DISK and use FITSOUT to write data
        to tape at end of night.\\
        (Maximum of 60 full size CCD frames per tape)
    

  \item {\bf{NORMAL OBSERVING}}\\         
        CCDSPACE \hspace{.5in} (to find out how much space is
        available on disk)\\
        PACKETS \hspace{.5in} (for data to be kept)\\
        To change TV filter settings use:\\
\begin{tabular}{||l|l|l|l||}    \hline
  TVF & 0 & clear & normal use\\
      & 1 & green & for seeing measurements \\
      & 2 & blue & useful for blue stars at high Z.D.\\
      & 3 & red & useful in bright moon \\  \hline
\end{tabular}\\
        CHANGE \hspace{.5in} (to change grating or anything else
        in IDS)\\
        RUN t ``NAME'' \hspace{.5in} (or CORRE if using preflash and you have 
        used this name for the procedure for t secs observation)\\
        MULTRUN n t ``NAME'' \hspace{.5in} (for n observations
        of t secs each)\\                            
        KILLMULTRUN \hspace{.5in} (if you want to stop MULTRUN for any reason)\\
        GLA t \hspace{.5in} (glance, or MIRA if using preflash; stores data 
        in temporary file R0)\\
        KEEP ``NAME'' \hspace{.5in} (keeps the last GLANCE run)\\
        RUNSTAT \hspace{.5in} (how long RUN has been going)\\
        DISP Rn \hspace{.5in} (to display an earlier run, number n)\\        
        If you want to keep the Grinnell image, ask the T.O. to
        ARCHIVE it for you.\\
        DISP An \hspace{.5in} (to display an archived TV image)\\
     
  \item {\bf{ON-LINE DATA REDUCTION}}\\
        SPECTRUM \hspace{.5in} (for quick-look on-line analysis,
        just follow the instructions)\\
        Use temporary files T1, T2, etc to store output spectra in, then\\
        PLOT T1 \hspace{.5in} and use default values for all plot
        parameters except Scale Factor, where values of 10-100 are
        likely to be needed. A plot appears on LEXIDATA.\\
        SPECPLOT T1 \hspace{.5in} as PLOT, but gives wavelength scale and 
        a cursor.\\
        When plot on LEXIDATA looks okay, use\\
        LEXPLOT \hspace{.5in} to get a hardcopy of it on the Printronix.\\
        (N.B. LEXPLOT takes 40-45 secs and should not be attempted close
        to the end of a run as it doesn't like you to use LEXIDATA 
        simultaneously).\\

  \item {\bf{Useful Hints}}\\
        Use CuNe arc for H$\alpha$ work, otherwise CuAr for red. This depends 
        on dispersion, look at Appendix C.\\
        Check that your flux standards are calibrated for $\lambda$
        $\geq$ 8000$\AA$. Look at Appendix A.\\
        F8 stars make good calibrators for removing atmospheric absorption
        bands for red spectra and are common.\\

  \item {\bf{BIAS FRAMES.}}\\
        RUN 0 ``BIAS'' \hspace{.5in}  ($\sim$5-10 times, when dark,
        for accurate estimation of bias)

  \item {\bf{PREFLASH FRAMES}} \hspace{.5in} (if needed)\\
        CORRE 0 ``PREFLASH'' \hspace{.5in} produces a RUN with PREFLASH 40
        units.\\
        SETFLASH 400\\
        RUN 0 ``FLASHMAP'' \hspace{.5in} produces a FLASH MAP of 400 units 
        (convenient if your default value is 40 units) 
        that you will scale to the used default value when reducing your
        data.\\

  \item {\bf{COPYING DATA.}}\\
        Fill in Tape Copy Request Form and place in tray with D tape for
        Duty Officer to collect; do it every morning, do not wait until your 
        final night.  The C tapes will appear in the INT 
        Visitors' pigeon hole.\\
        D.I.Y.:\\
        FITSINIT \hspace{.5in} (INTD\_\_\_) for first time use.\\
        FITSOUT \hspace{.5in} (e.g. R1-R60) data is written to tape in 
        International FITS standard since 16th January 1989; see Appendix B.


\end{list}
\bigskip
\subsection{Morning Activities.}

\begin{list}%
 {--}{\setlength{\rightmargin}{\leftmargin}}
             
  \item {\bf{CLOSEDOWN.}}\\
        Dump all data to tape\\
        SHUTDOWN\\
        Stop ICS computer (see notes on wall in the tape-drive's room).\\
        Telescope Operator will refill liquid nitrogen in CCD cryostat.\\
        Fill in tape request form (and feedback form on your last
        night).\\
        Go to bed.\\
\end{list}                  
\section{Observing with the Cross-disperser}

\subsubsection{Mounting the Cross-disperser}

The cross-disperser is mounted next to the folding prism; it will have been
done by the SA following this procedure:

\begin{list}%
 {--}{\setlength{\rightmargin}{\leftmargin}}
             
\item Remove the lid at the bottom of the IDS.
\item         One of the {\bf three} mounting screws has been marked A, hold it
        in front of the corresponding hole and then rotate the unit 120\DEG
        counterclockwise.
\item         Insert the unit and rotate 120\DEG back.
\item         Fasten screws and put lid back.
\item         Keep calm. It might take 1/2 an hour to do it the first time.
\end{list}        
\subsubsection{Tips for Observing with the Cross-disperser}

Here are some practical tips for observing with the Cross-disperser.
\begin{list}%
 {--}{\setlength{\rightmargin}{\leftmargin}}
             
  \item Focusing is best done with a R1200Y grating and the Copper Neon lamp.
\item         There is no software to extract the orders on-line, however,
              FOS software can be used afterwards to extract about three
              orders. This is easily done because they are {\bf straight
              lines} (see figure~4.10).
\item    Wavelength calibration is rather difficult due to the lack of a
         lamp with wide wavelength coverage. A planetary nebula (such as
         NGC~7027) can be used. Figure~4.10 shows maps of the CCD images for
         grating angles of 60.75\DEG , 60\DEG and 59.25 \DEG with enough
         lines even in the ultraviolet. See also Table~3.3.
\item    Do not use a grating angle outside the range 60 $\pm$ 1 \DEG ,
         otherwise the efficiency falls off rapidly.
\item    The FOS-dekker is best used, in order to ensure that there is no
         overlap of orders in the spatial direction. It has a 24.5 arcsec
         long slit which is ideal for use with the cross-disperser.
\end{list}

\begin{figure}[p]
\vskip 20cm
\caption[(a) A spectrum from the IDS cross-disperser]
{(a) A spectrum using the IDS cross-disperser and a grating angle 60.75\DEG . 
Orders (3) to (8)  can be seen.}
\end{figure}

\begin{figure}[p]
\addtocounter{figure}{-1}
\vskip 20cm
\caption[(b) Grating angle 60.\DEG ]
{(b) A spectrum using the IDS cross-disperser and a grating angle 60.\DEG . 
Orders (3) to 8  can be seen.}
\end{figure}

\begin{figure}[p]
\addtocounter{figure}{-1}
\vskip 20cm
\caption[(c) Grating angle 59.25\DEG ]
{(c) A spectrum using the IDS cross-disperser and a grating angle 59.25\DEG . 
Orders 3 to 8  can be seen.}
\end{figure}
\vfill
